Martian Phyllosilicates: Recorders of Aqueous Processes (2008) 7042.pdf

SYNTHESIS OF CLAY MINERALS AND THE RELATIONSHIP WITH FORMATION PROCESSES AND CRYSTAL CHEMISTRY. P. Andrieux1 , S. Petit1, and A. Decarreau1, 1HydrASA, Université de Poitiers, 40 avenue du Recteur Pineau, 86022 Poitiers Cedex, [email protected], sabine.petit@univ- poitiers.fr

under partially reducing or oxidizing conditions using Different approaches have been used for the coprecipitated gels of silica and FeSO4 at low determination of the mineralogy at the Mars surface. temperature below 150°C. But they obtained “defect The direct measurements with spacecraft, the nontronite”. Several authors described the synthesis of study of Martian meteorites, and the laboratory nontronites but obtained poorly crystalline nontonites measurements on analogue materials have permitted to or in very diluted solutions [4, 5, 6, 7, 8]. determine the Martian soil composition. Thanks to Recently, we obtained synthetic nontronites using theses different approaches, clays and clay minerals coprecipitated gels containing Si, Al and Fe. -rich have been discovered on Mars surface [1]. nontronites with different rates of are Several smectites have been identified. The main obtained. phyllosilicates on Mars are the iron-rich clays as Using Clay minerals synthesis, we can better nontronite. But Mg- and Al-rich members are also determine the condition of formation of equivalent present and have been detected on Mars’ surface for natural clays knowing their physical and chemical example as and . Clay conditions of synthesis. minerals on Mars can compare to Earth’s analogues Furthermore, synthetic clays can be used as which could permit to understand the condition of reference samples for spectroscopic interpretations. formation and crystal chemistry [2]. Analogue Martian clay minerals synthesized in Three processes are important in the origin of clay laboratory could lead very important research on the minerals. Under the condition of the earth’s surface, formation of this clays and their crystallochemistry. the alteration of other silicate minerals could lead to the formation of clay minerals. At pressures or temperatures higher than those of the earth’s surface, References: clay minerals are the result of recrystallisation [1] Chevrier V. and Mathe P. E. (2006) Planetary processes. And, precipitation from solution is the third and Space Science, 55, 289–314. [2] Poulet F. and al. process. For theses different processes, aqueous (2005) Nature, 438, 623–627. [3] Velde B. (1992), solution plays a major role in the formation of clays in 198p. [4] Kloprogge J. T. et al. (1999) Clays and Clay natural and synthetic system [3]. minerals, 47, 529–554. [5] Caillère et al. (1953) Clay minerals synthesis is useful to the Comptes rendus de l’Academie Sciences (Paris), 237, understanding of formation processes in nature on 1724–1726. [6] Caillère et al. (1955) Bulletin de la Earth and Mars. Synthesis at low temperatures can Societe Francaise de Mineralogie et Crystallographie, permit to understand the formation processes in 78, 227–241. [7] Decarreau and Bonnin (1986) Clay surface. minerals, 21, 861–877. [8] Decarreau et al. (1987) The clay minerals which were already evidenced Clays and clay minerals, 22, 207–223. on Mars could be possibly synthesized in laboratory. The conditions of formation of clay minerals in synthetic systems depend on pH, temperature, pressure, starting materials and element concentrations. For example, regarding nontronites, their synthesis have been realized in the past by Caillère and al. (1953, 1955) mixing dilute solution of silica, iron (II) or (III) chlorides, and salts of Mg and Al at low temperature (100°C) and adjusting pH between 8,5 and 9,5. They obtained very diluted suspensions of nontronites. Hamilton and Furtwängler (1951) obtained also very diluted suspensions of nontronite using sodium metasilicate and iron (III) chloride at high temperature. Decarreau and Bonnin (1986) or Decarreau and al. (1987) synthesized ferric smectite